Feature: Nuts and bolts - Diamond synchrotron
29 November 2012. By Meredith Thomas
Light is not a resource you would expect to find in short supply. However, the intense beams of electromagnetic radiation required for a wide range of experimental techniques are so finely tuned that an international team of experts is required to generate them.
Diamond Light Source, opened in 2007, was built to supply scientists and industry with just this capability. The facility currently supplies 20, soon to be 22, experimental stations with beams of X-rays, ultraviolet light and infrared light needed for a variety of purposes.
Diamond is an example of a third- generation synchrotron. The device works by accelerating electrons to 3 gigaelectronvolts (GeV). These are then channelled into a storage ring, which they travel round at close to the speed of light.
The storage ring is not quite circular: instead, it is a series of straight lines. Every time the electrons turn a corner, they release energy in the form of electromagnetic radiation, or light. This light is fed to a beamline, where it can be used in experiments.
The facility was funded by a partnership between the government and the Wellcome Trust, and is free to academic scientists at the point of access. Ten per cent of proprietary beamtime is available to industrial scientists at a cost. All in all, around 3000 researchers use the Diamond synchrotron each year.
Experiments carried out generally involve focusing synchrotron light onto a substance (be it solid, liquid or gas) and measuring what happens to the light, using techniques such as diffraction, spectroscopy and imaging. This can provide valuable information about the chemical composition or atomic structure of the substance.
The Diamond synchrotron is used in fields as diverse as chemistry, archaeology, cell biology, energy and the environment, and materials science. Funding has been allocated to construct a further 10 beamlines by 2018, allowing Diamond to reach its full potential.
This feature also appears in issue 72 of ‘Wellcome News’.
Parts of the Diamond sychrotron
A beam of electrons is generated by an electron gun, which is a high-voltage cathode heated in a vacuum. The electrons are then accelerated by a linear accelerator to 1 GeV before entering the booster synchrotron.
Diamond's second particle accelerator, this contains 36 bending magnets that keep the electrons moving around the curved parts of the booster, and a radiofrequency voltage source to help the electrons accelerate in the straight parts. Here, the electrons reach up to 3 GeV.
This has 24 angled sections, with 48 bending magnets to keep electrons within the boundary of the 560-metre circumference of the track at energies of 3 GeV. The electrons generate synchrotron light as they speed around the ring. Electrons stay in the ring for some 20 hours.
From the storage ring, light is channelled into an optics hutch, to filter and focus the beam, and then on to an experimental hutch filled with sensors and detectors.
The electrons lose energy as they move around the ring generating synchrotron light. The cavity contains an electromagnetic field that oscillates at radio frequencies, which replaces this lost energy and ensures the electrons stay on track around the storage ring.
The site's main building is linked to the storage ring by a first-storey bridge. It houses many of Diamond's 450 staff, and provides facilities for the researchers who visit each year.
Top image: An illustration of the Diamond synchrotron facility. Credit: Bret Syfert.
Right-hand image: The Diamond Light source building at dusk. Credit: Diamond Light Source